Two macromolecular effectors of ornithine decarboxylase (ODC: L-ornithine carboxy-lyase, EC 4.1.1.17) have been extracted from an ODC-(SpeC-) mutant, Escherichia coli MA255. One of these is an ODC inhibitor, M.W. 15,000 plus or minus 2,000 that is labile to trypsin, its activity increases 20 fold in response to increased polyamine levels of the growth medium. It has additional characteristics similar to those of the ODC antizyme of eukaryote cells; it is a non-competitive inhibitor of ODC; the complex formed between ODC and the ODC inhibitor can be dissociated with salt to provide active ODC and active ODC inhibitor; furthermore, this E. coli ODC inhibitor is inhibitory to eukaryote ODC. A thermostable macromolecule that activates ODC in vitro has been extracted from MA255; increased polyamine levels of the growth medium caused a 1.6 fold increase in the activity of this ODC activator. Macromolecules with comparable activities have also been identified in the parent ODC ion (SpeC ion) strain MA197. These two activities will be purified and their role in the control of ODC will be determined, as well as their mode of induction and interaction and the loci of the associated structural regulatory genes. The methodology to be used will include standard biochemical genetic techniques such as protein purification, amino acid analysis, enzyme assays, gene mapping using mutants and amplification of the cellular levels of ODC inhibitor and activator using transducing phages.